Conventional power generating stations, or power plants, can use steam turbines to generate power. In a conventional power plant, steam generated in a boiler is fed to a turbine where the steam expands as it turns the turbine to generate work to create electricity. Occasional maintenance and repair of the turbine system is required. During turbine maintenance periods, or shutdown, the turbine is not operational. It is typically more economical to continue boiler operation during these maintenance periods, and as a result, the power plant is designed to allow the generated steam to continue circulation. To accommodate this design, the power plant commonly has supplemental piping and valves that circumvent the steam turbine and redirect the steam to a recovery circuit that reclaims the steam for further use. The supplemental piping is conventionally known as a turbine bypass.
In turbine bypass, steam that is routed away from the turbine must be recovered or returned to water. The recovery process allows the power plant to conserve water and maintain a higher operating efficiency. An air-cooled condenser is often used to recover steam from the bypass loop and turbine-exhausted steam. To return the steam to water, a system is required to remove the heat of vaporization from the steam, thereby forcing the steam to condense. The air-cooled condenser facilitates heat removal by forcing low temperature air across a heat exchanger in which the steam circulates. The residual heat is transferred from the steam through the heat exchanger directly to the surrounding atmosphere.
Because the bypass steam has not produced work through the turbine, the steam pressure and temperature is greater than the turbine-exhausted steam. As a result, bypass steam temperature and pressure must be conditioned or reduced prior to entering the air-cooled condenser to avoid damage. Cooling water is typically injected into the bypass steam to moderate the steam's temperature. To control the steam pressure prior to entering the condenser, control valves, and more specifically, fluid pressure reduction devices, commonly referred to as spargers, are used. The spargers are restrictive devices that reduce fluid pressure by transferring and absorbing fluid energy contained in the bypass steam. Conventional spargers are constructed of a cylindrical, hollow housing or a perforated tube that protrudes into the turbine exhaust duct. The bypass steam is transferred by the sparger into the duct through a multitude of fluid passageways to the exterior surface. By dividing the incoming fluid into progressively smaller, high velocity fluid jets, the sparger reduces the flow and the pressure of the incoming bypass steam and any residual cooling water within acceptable levels prior to entering the air-cooled condenser.
In the process of reducing the incoming steam pressure, the spargers transfer the potential energy stored in the steam to kinetic energy. The kinetic energy generates turbulent fluid flow that creates unwanted physical vibrations in surrounding structures and undesirable aerodynamic noise. In power plants with multiple steam generators, multiple spargers are mounted into the turbine exhaust duct. Because of space limitations within the duct, the spargers are generally spaced very closely. Additionally, the fluid jets, consisting of high velocity steam and residual spray water jets, exiting the closely spaced spargers can interact to substantially increase the aerodynamic noise. In an air-cooled condenser system, turbulent fluid motion can create aerodynamic conditions that induce physical vibration and noise with such magnitude as to exceed governmental safety regulations and damage the steam recovery system. The excessive noise can induce damaging structural resonance or vibration within the turbine exhaust duct. Therefore, it is desirable to develop a device and/or a method to substantially reduce these harmful effects.
FIG. 1 illustrates a conventional power plant employing a turbine bypass system 100. A boiler or re-heater 102 generates steam. The steam can travel through a turbine 104 to generate rotational mechanical energy and power a generator 114 to create electricity. The steam then continues through the turbine 104 to a condenser 106 before returning to the boiler or re-heater 102. In bypass mode, the steam travels through a bypass valve 108 with additional water supplied by a bypass water valve 110, before entering the condenser 106. A digital controller 112 controls the operation of the bypass valve 108 and the bypass water valve 110. A sparger assembly can be included along the bypass path after the bypass valve 108 to condition the steam prior to entering the condenser 106. The sparger assembly can often generate a substantial amount of noise as the steam pressure and temperature are reduced.